Increasing the ratio of omega-3 to omega-6 fatty acids in the diet appears to slow the progression of prostate cancer, according to the results of an animal study.

The so-called Western diet commonly consumed in the US contains mostly omega-6 fatty acids, derived from corn oil and other sources. Omega-3 fatty acids, by contrast, are abundant in cold-water fish, a food source missing in the diets of many Americans.

"Our study showed that altering the fatty acid ratio found in the typical Western diet to include more omega-3 fatty acids and decreasing the amount of omega-6 fatty acids reduced prostate cancer tumor growth rates and PSA levels in mice," senior author Dr. William J. Aronson, from the University of California, Los Angeles School of Medicine stated.

Aronson noted that the Western diet usually contains an omega-6 to -3 ratio of about 15 to 1. In the current study, comparison animals received a diet containing a similar ratio, while intervention animals were given a diet with a ratio of about 1 to 1.

Aronson believes that with dietary changes and the use of fish oil supplements, an omega-6 to -3 ratio of 2 to 1 or possibly lower is attainable in prostate cancer patients.

The new study, reported in Clinical Cancer Research, involved mice implanted with human prostate cancer cells. Aside from the difference in the omega-6 to -3 ratio, all of the animals received identical 20 percent fat diets.

Tumor growth rates, the final tumor size, and PSA levels were all lower in the intervention group compared with mice given Western diets. Laboratory testing showed that cancer cells grew 22 percent slower in culture dishes containing body fluid from the intervention group. Consumption of the increased omega-3 diet was also associated with an 83% reduction in tumor prostaglandin E (PGE)-2 levels, a chemical known to promote inflammation.

"This is an initial animal-model study that is one of the first to show the impact of diet on lowering an inflammatory response known to promote prostate tumor progression in tumors. More research needs to be done before clinical recommendations can be made, but the finding is significant," Aronson noted.

"At this point we would not recommend changing fatty acid intake for prostate cancer patients. However, we are conducting a randomized study in men to test if dietary changes affect prostate tissue levels of COX-2 and PGE-2," he added.

SOURCE: Clinical Cancer Research, August 1 2006.